A possible association of hematologic malignancy with hereditary nonpolyposis colon cancer reported in the literature, together with a report that MSH2-deficient mice are susceptible to malignant lymphoma, strongly supports the finding that this patient's lymphoma was related to hereditary nonpolyposis colon cancer. Overall, this case manifested a distinct clinical course similar to that observed in an animal model that is deficient in DNA mismatch repair machinery, thus providing scientific and clinical implications for understanding the molecular basis of these tumors and for critical management of hereditary nonpolyposis colorectal cancer patients, respectively.